The overall objective of the proposed study is to elucidate the physiological role of adenosine diphosphoribosylation of proteins during progesterone-induced maturation of Xenopus oocytes. When radiolabelled NAD ion is microinjected into oocytes, the radioactive material bound to protein is found primarily in the cytosol, while little, if any, is incorporated into the germinal vesicles. This finding was unexpected and is the first evidence for the occurrence of ADP-ribosylation of proteins in the cytosol of oocytes. The molecular mechanism of this reaction will be investigated. To accomplish this goal, there will be studies of the subcellular site of the ADP-ribosylating activity, characterization of this enzyme system, identification of the acceptor protein(s), and delineation of its functional role in the maturation. The investigation will be performed on oocytes undergoing growth and maturation. The anticipated information will clarify the functional role of this post-translational modification of proteins in the induction of germinal vesicle breakdown.